The growing importance of wavelength division multiplexing (WDM) has exerted a need for a variety of optical components for various functions important to the quality of such networks.
In particular, in WDM optical networks it may be necessary to provide equalizers to compensate for differences in signal power levels in the multiple channels of a WDM transmission system. Such differences may arise, for example, because of loss variations or non-linear effect in optical fibers or non-flat gain spectra in optical amplifiers. Moreover, in optical networks, signals originating from different modes or taking different paths may need to be combined at some point and so require adjustment or equalization in their power levels. An example of equalization of multiple channels of a WDM transmission system is described in U.S. Pat. No. 5,745,271 that issued on Apr. 28, 1998 to J. E. Ford, D. A. B. Miller, M. C. Nuss and J. A. Walker.
Equalizers can also be used at WDM transmitter locations to provide channel equalization, or pre-emphasis, before the signals are launched into the transmission system. WDM equalizers could also be useful in optical network components, such as a cross-connect where signal equalization might improve cross-talk and signal-to-noise ratios.
Also important in a WDM optical network is the optical monitoring function to monitor optical spectra, particularly as the number of channels increases, wavelength tolerances narrow, and systems evolve towards all-optical networks.
Of increasing interest for such functions has been the use of micromechanical optical devices because of potential greater ruggedness, longer life and lower costs that such devices promise. Such devices show great promise in applications where the action is not especially wavelength dependent, as for example in the control of the total power level of a multichannel signal rather than of individual components.
There currently are available optical components that have been developed for use in video and computer projections that comprise two-dimensional arrays in horizontal rows or vertical columns of single-axis tilting digitally (bistable) settable micromechanical mirrors, such as the Digital Micromirror Device (DMD). These have been commercialized for use in video and computer projection systems in large arrays (greater than 800.times.600 pixels). Each pixel in the array, for example, may comprise a 16.times.16 micron aluminum-coated mirror that is separately addressable and can be tilted, for example, plus or minus ten degrees electronically. The pixel spacing may be 17 microns, resulting in an overall fill factor of about ninety percent. Moreover, it appears likely that further improvements will be forthcoming that will permit smaller size with similarly tight packing.